1. Field of the Invention
The present invention relates to a fuel injection nozzle, for an internal combustion engine, that is needed to be fastened or connected to a high-pressure fuel rail to inject fuel directly into a cylinder.
2. Description of the Related Art
A method of connecting a high-pressure fuel pipe to a device included in a high-pressure fuel system is disclosed in Jpn. Pat. No. 3385415 (Patent Document 1). This method presses a tapered end part of a high-pressure fuel pipe against a tapered fuel port formed in a device included in a high-pressure fuel system by high pressure. The high-pressure fuel pipe is a double-wall pipe having an inner pipe of a stainless steel, and an outer pipe of a soft steel surrounding the inner pipe. An end part of only the outer pipe is pressed against the tapered fuel port so that the end part of the outer pipe undergoes plastic deformation so as to conform to the shape of the tapered fuel port to improve fuel-sealing performance of the joint of the high-pressure fuel pipe and the device of the high-pressure fuel system.
A method of connecting a fuel injection nozzle to a fuel rail disclosed in JP-A 2005-98275 (Patent Document 2) forms a thin part in a member of the fuel rail to prevent the breakage of the member by reducing stress that may be induced in the member by an assembling error when the fuel injection nozzle is connected to the fuel rail.
Patent Document 1: Jpn. Pat. No. 3385415
Patent Document 2: JP-A 2005-98275
A fuel injection nozzle for a direct injection system is screwed in an injector hole formed in the cylinder head of an internal combustion engine. The fuel injection nozzle is in direct contact with the cylinder head or in indirect contact with the cylinder head through a metal member having a comparatively large modulus of elasticity. The fuel injection nozzle is connected to a fuel pipe. The fuel pipe presses the fuel injection nozzle through an elastic member. The fuel injection nozzle is driven in a state where the pressure of the fuel (hereinafter, referred to as “fuel pressure”) presses the fuel injection nozzle against the cylinder head while the engine is in operation.
The fuel injection nozzle generates sounds when the fuel injection nozzle is driven to open and close the nozzle valve. The generated sounds cause the valve body of the fuel injection nozzle to vibrate in directions parallel to the axis of the nozzle valve. As mentioned above, the fuel injection nozzle is pressed against the cylinder head by a force acting in a direction parallel to the axis of the nozzle valve. Both the cylinder head and the component members of the fuel injection nozzle are made of metals, in which sounds propagate at nearly equal velocities, and sound waves propagate easily through the cylinder head and the fuel injection nozzle. Thus the sound generated by the fuel injection nozzle propagates easily to the cylinder head. Sounds propagated to the cylinder head vibrate the cylinder head and devices attached to the cylinder head to generate noise. Therefore, it is desirable that the fuel injection nozzle and the cylinder head have greatly different moduli of elasticity, respectively, or that the fuel injection nozzle is connected through a member in which sounds propagate at a velocity different from a velocity in which sounds propagate in the fuel injection nozzle to the cylinder head.
A method of attaching the fuel injection nozzle to the cylinder head such that the fuel injection nozzle is not in contact with the cylinder head with respect to a direction parallel to the axis of the nozzle valve and a method of attaching the fuel injection nozzle through a substance having low rigidity, in which sounds propagate at a low velocity, to the cylinder head are effective in attaching the fuel injection nozzle to the cylinder head in the forgoing mode. This method needs to use a fuel rail for fixating the fuel injection nozzle. The fuel rail is fixed to the cylinder head, the fuel injection nozzle is fixed to the fuel rail, and a sealing member for sealing the gap between the fuel injection nozzle and the cylinder head to prevent the leakage of combustion gas is put on an end part of the fuel injection nozzle to form a shaft seal part.
When the fuel injection nozzle is thus fixed to the fuel rail, a fixing member for fixating the fuel injection nozzle needs to bear force produced by the fuel pressure. Therefore, the fixing member needs to have high strength. The fuel rail, as compared with the fuel injection nozzle, is a highly rigid member. Therefore, the fuel injection nozzle is attached rigidly to the fuel rail.
There is an error between the position of a mounting hole formed in the fuel rail to receive the fuel injection nozzle and the position of a mounting hole formed in the cylinder head to receive the fuel injection nozzle. It is not easy to form the mounting hole for receiving the fuel injection valve in the fuel rail manufactured by welding steel members at a desired position in high accuracy as compared with forming the mounting hole which can be formed at a desired position in the cylinder head usually by machining in high accuracy.
Consequently, the fuel injection nozzle is fitted in the mounting hole of the cylinder head and mounting hole of the fuel rail which are not aligned with each other. Therefore, when the sealing member put on the end part of the fuel injection nozzle on the side of the nozzle hole of the fuel injection nozzle rigidly attached to the fuel rail is fitted in the mounting hole of the cylinder head, the front end part of the fuel injection nozzle is displaced forcibly relative to the mounting hole of the fuel rail.
Thus, a bending moment acts on the fuel injection nozzle and deforms the fuel injection nozzle forcibly. Consequently, it is possible that internal parts of the fuel injection nozzle holding movable members are deformed affecting the characteristics of the fuel injection nozzle including injection volume.
If the walls of the internal parts holding the movable members are formed in a sufficiently big thickness to avoid such troubles, those parts will be forcibly displaced and other members will be deformed. The fuel injection nozzle defines a fuel passage for carrying the fuel to the nozzle hole of the fuel injection nozzle. Therefore, the fuel injection nozzle needs to be designed so as to withstand the fuel pressure. If members other than the internal movable members of the fuel injection nozzle are formed so as to be deformable, an excessively high stress is induced in the deformed members. Consequently, the members are liable to be broken and cannot withstand a high fuel pressure.
The foregoing problems will not arise if the fuel rail is formed sufficiently accurately. However, an accurate fuel rail is difficult to manufacture and is very expensive.
The high-pressure fuel pipe fastening method disclosed in Jpn. Pat. No. 3385415 uses a soft material and a hard material in combination for fastening the high-pressure fuel pipe and tapers an end part of the pipe to form a plastically deformable part to ensure a fuel sealing effect even if the fuel pipe is not aligned with the tapered fuel port formed in the device. However, nothing is disclosed in Jpn. Pat. No. 3385415 about the effect of the fastening part and the forcible displacement or deformation on the body of the fuel injection nozzle.
The method disclosed in JP-A 2005-98275 forms a part having a small wall thickness in the fuel rail to absorb deformation in the fuel rail. However, a method of ensuring strength sufficient to withstand fuel pressure and absorbing deformation is not satisfactorily taken into consideration.